Variable gain fluidic device



March 17, 1970 L. R. KELLEY 3,500,848

VARIABLE GAIN FLUIDIC DEVICE Filed Feb. 28. 1967 4 g m $774M United States Patent 3,500,848 VARIABLE GAIN FLUIDIC DEVICE Lonny R. Kelley, Ballston Lake, N.Y., assiguor to General Electric Company, a corporation of New York Filed Feb. 28, 1967, Ser. No. 619,362 Int. Cl. Fc 1/14, 1/12 US. Cl. 137-81.5 3 Claims ABSTRACT OF THE DISCLOSURE A two-dimensional flow fluidic device has two interconnected analog fluid amplifiers of the single receiver type with the power fluid inlets connected to a source of differentially pressurized fluid input signals to be ampli fied. First control fluid inlets are connected to a common source of pressurized fluid adjustable in pressure to determine the operating region of the fluid amplifiers. A pair of opposed vent passages are located adjacent the fluid receiver in each amplifier. Additional venting may be provided by connecting another vent passage to a second control fluid inlet in each amplifier. The differential pressure of the fluid received in the fluid receivers is the output of the device representing the amplified input signal, and the gain is some value less than unity as determined by the pressure of the fluid supplied to the first control fluid inlets.

My invention relates to fluid amplifier devices, and in particular, to a fluidic device which provides a controllably variable gain function.

The recently developed fluid control devices known as fluid amplifiers (or fluidic devices) having no moving mechanical parts have many advantages over analogous electronic devices. In particular, the fluid amplifier is relatively simple in design, inexpensive in fabrication, capable of withstanding extreme environmental conditions such as shock, vibration, nuclear radiation and high temperature, and the no-moving parts feature permits substantially unlimited lifetime thereby achieving long periods of uninterrupted operation. These fluidic devices may be employed as analog and digital computing and control circuit elements, and also as power devices to operate valves and the like. Two broad classes of fluid amplifiers are the analog-type and the digital-type, the subject invention being limited to the analog-type device. The analog fluid amplifier is commonly referred to as the momentum-exchange type wherein a pressurized fluid stream or jet to be controlled, hereinafter described as the power (fluid) jet, is deflected by one or more control fluid jets directed laterally at the power jet from opposite sides thereof. In the most conventional amplifier, the power jet is normally directed midway between two fluid receivers and is deflected relative to the receivers by an amount proportional to the net sideways momentum of the control jets. This device is therefore commonly described as a proportional or analog device.

The conventional two-receiver analog fluid amplifier is of the constant gain type wherein the gain may be defined as the change in pressure of the fluid received by the receivers corresponding to a predetermined change in the pressure of the fluid supplied to the control fluid inlets. Such conventional constant gain fluid amplifier is a two-dimensional flow device in that the flow paths of the various power and control jets are all coplanar. An example of a variable gain fluid amplifier is described in US. Patent 3,186,422 to W. A. Boothe, in which an additional gain changing control fluid jet provides a deflection of the power jet in a third dimension, that is, in a direction normal to the deflection produced by the first control jets. This latter fluid amplifier is a more complex structure in that it requires an additional control fluid inlet for generating the gain changing control jet and additional fluid receivers.

Therefore, one of the principal objects of my invention is to provide a variable gain fluidic device having a simple structure.

Another object of my invention is to provide a variable gain fluidic device which utilizes only a two dimensional deflection of the power fluid jet to obtain the variable gain feature.

A further object of my invention is to provide suclm device with a gain which is controllably variable to values less than unity. A similar device, but having a gain controllably variable to values greater or less than unity, is the subject of a concurrently filed patent application S.N. 619,361 to M. C. Doherty, and assigned to the assignee of this application.

Briefly summarized, my invention is a fluidic device including a single fluid amplifier of the analog type when utilizing single-sided input signals or two such amplifiers interconnected for use with push-pull signals. The fluid amplifiers each comprise a power fluid inlet, a single fluid receiver aligned with the centerline axis of the amplifier, and at least one control fluid inlet coplanar with the power fluid inlet and receiver for controllably deflecting by momentum exchange the power jet relative to the receiver. A pair of opposed vent passages are employed for relieving the fluid pressure adjacent the receiver. In the case of the device utilizing double-sided (push-pull) input signals, the power fluid inlets are in communication with a source of variable and differentially pressurized fluid representing a push-pull input signal to be amplified. First control fluid inlets are in communication with a common source of fluid adjustable in pressure within a predetermined range of pressures and representing a bias signal which determines the operating region of the input signal in relationship to the nonlinear inputoutput characteristic curves of the fluid amplifiers. Second control fluid inlets, if employed, are disposed in opposed relationship to the first control fluid inlets and are connected to additional vent passages. The gain of my two-dimensional flow device is a function of the bias signal and is controllably variable to values less than unity by adjustment of the pressure thereof.

The features of my invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic representation of a push-pull embodiment of the variable gain fluidic device constructed in accordance with my invention;

FIGURE 2 is a schematic representation of the device illustrated in FIGURE 1;

FIGURE 3 is a graphical representation of the nonlinear control input-output characteristics for a singlereceiver analog fluid amplifier of the type employed in the device of FIGURE 1 for various power fluid supply presanalog type, also described as single-receiver amplifiers,

which are adapted for use with a diflerentially pressurized (push-pull) input fluid signal to provide at the outputs thereof a correspondingly amplified push-pull output signal. The device may also be employed with a single-sided input signal to provide an amplified single-sided output signal but in the latter case it is more economical to construct the device from only one of the fluid amplifiers, that is, to employ only one half of the device of FIGURE 1. The two fluid amplifiers are illustrated as a whole by numerals 5 and 6 and details of the structure and operation of similar analog-type fluid amplifiers, and the external connections, are provided in US. Patents 3,233,622 and 3,260,456 to W. A. Boothe, whereas, the particular fluid amplifier is disclosed in a copending US. patent application S.N. 499,403 to W. A. Boothe et al., filed Oct. 21, 1965, and assigned to the same assignee as the present invention. It will suffice to describe the fluid amplifiers herein as each being provided with a power fluid inlet, at least one control fluid inlet, a single fluid receiver and at least a pair of vent passages adjacent the receiver.

The power fluid and control fluid inlets each comprise a fluid passage in communication with a source of pressurized fluid at a first end thereof and terminating in a fluid flow restrictor or nozzle for issuing a jet therefrom at a second end thereof. Thus, the power fluid inlets of amplifiers 5 and 6 respectively comprise fluid passages 7 and 17 in communciation at first ends thereof with a source of variable and diflerentially pressurized fluid signals P P (AP wherein the magnitude of differential pressure between this pair of signals represents an input signal to be amplified. The supply pressure P of this variable pressurized power fluid is actually an average pressure P with a variable pressure AP, representing the input signal to be amplified superimposed thereon (P p-l-AP The push-pull (differentially pressurized) input signal P, P is of the analog type, that is, variable in magnitude of pressure generally as a function of some system parameter. Passages 7 and 17, respectively, terminate at second ends thereof in fluid flow restrictors (nozzles) 9 and 19 for generating variable and diflerentially pressurized streams or (power) jets of fluid issuing from such nozzles and directed along the centerline axis of the fluid amplifiers. The centerline axes of amplifiers 5 and 6 are defined respectively as the straight lines along which nozzle 9 and downstream fluid receiver 10, and nozzle 19 and receiver 11 are aligned. In like manner, first control fluid inlets of amplifiers 5 and 6, respectively, comprise fluid passages 21 and 24 terminating in fluid flow restrictors 23 and 26 for generating bias control jets of fluid issuing therefrom and directed substantially laterally at the power jet. Passages 21 and 24 are in communication with a common source of fluid P adjustable in pressure within a predetermined range of pressures.

The control jets issuing from nozzles 23 and 26 represent a bias signal which determines an operating region of the input signal AP, in relationship to the nonlinear control input-output characteristic curves of the fluid amplifiers. A family of such characteristic curves for a single amplifier is illustrated in FIGURE 3 wherein the. abscissa P represents the bias signal pressure and the ordinate P represents the output pressure (pressure of fluid received in the fluid receiver). The curves are all plotted for a single constant amplifier load, and each curve is plotted for a different average power fluid Supply pressure '1 all pressure being on pounds per square inch gage (p.s.i.g.). The alignment of the power nozzle and the receiver is evident from the characteristic curves since at zero bias pressure, P =0, a maximum output pressure P is recovered in the receiver. With increased positive or negative bias pressures, the output pressure decreases in a nonlinear manner as illustrated. The gain of the amplifier is determined from the change in the output pressure AP corresponding to a predetermined change in power fluid (input signal) supply pressure AP for a constant bias pressure P Thus, at a first (relatively low) bias pressure P the gain is AP /AP or for the example of FIGURE 3. At a second (relative y high) bias pressure P the gain is reduced to due to the nonlinearity of the curves. In all cases the gain is less than unity since the pressure P recovered in the receiver is always less than the power fluid supply pressure P The nonlinearity of the curves is due primarily to the amplifier geometry wherein the power nozzle width, receiver width and distance from power nozzle to receiver define the maximum pressure recovery in the receiver for each power fluid supply pressure condition. It is this nonlinear feature of this fluid amplifier which permits its use as a variable gain device. Small signal operation of each fluid amplifier in my device is assumed in order to obtain a constant gain for each bias signal pressure, and, the operating point of the fluid amplifier is determined by such bias signal pressure P and the average pressure I of the power fluid supply pressure P The pressure P of the bias control fluid can be adjusted manually or automatically (by means of a suitable valve connected between the supply and passages 21, 24) as determined by the particular fluidic circuit of which the subject device forms a part thereof. Thus, the gain of the particular fluidic circuit may be controllably varied in response to a particular magnitude or desired limit of a system parameter, or as a function of a particular system parameter. As one example, my variable gain device finds use in a fluidic jet engine control system where the gain in one part of the system is sensitive to engine loading and temperature effects, and my device functions as a gain equalizer to nullify this particular gain sensitivity.

Two pair of opposed vent pasages 28, 29 and 30, 31 are located adjacent the receiver on opposite sides of the centerline axes in amplifiers 5 and 6, respectively. The outer terminal ends of the vent passages, designated V, are in communication with a selected medium such as the ambient atmosphere, or, in the case Where the fluid employed is a liquid, a return passage to the sump of the pressurized fluid supply. The vent passages relieve fluid pressure adjacent the receivers in that the fluid of the power jet which does not directly impinge on the fluid receiver is directed away therefrom to the vent passages. The fluid received in fluid receivers 10 and 11 is thus a diflerentiall pressurized push-pull output fluid signal designated P P (AP which represents the amplified variable input signal AP Vent passages 28 and 31 may have their upstream side wall 32 and 33 respectively oriented such that the inner terminal ends of vent passages 28 and 31 include the region opposite the bias control nozzles 23 and 26 (not shown). An additional venting in this region is highly desirable to prevent the generation of back pressure therein. A ternatively, control nozzles 34 and 35 disposed in opposing relationship to nozzles 23 and 26 may be employed as inner terminal ends of additional vent passages 36 and 37 in amplifiers 5 and 6, respectively, as shown.

A schematic representation of my FIGURE 1 device is illustrated in FIGURE 2 where the various pressurized input and output fluid signals and sources are indicated by the notation employed in FIGURE 1, it being understood that the power fluid supply pressure P in both figures is actually an average pressure I and the variable pressure input signal AP =P -P superimposed thereon. The operation of my device will now be explained.

The device is assumed to be constantly supplied with a pressurized power fluid having an average pressure P and the variable pressure AP, representing the input signal S to be amplified superimposed thereon. The constant pressure control fluid bias signal P offsets the power jets relative to the centerline axes of the receivers in the same manner as in the more conventional fluid amplifier operation wherein the power fluid supply pressure is constant and the control fluid signals are variable. Thus, the bias signals in the amplifiers cause deflections of the two power jets' a proportional amount as determined by the relative instantaneous magnitudes of the power fluid and bias supply pressures. For a particular bias pressure, a low pressure power jet is deflected to a greater degree away froin the centerline axis of the amplifier than would a higher pressure power jet due to momentum-exchange principles. Hence, the variable input signals P and P cause deflections of the power jets relative to their constant bias or offset positions determined by the magnitude of the pressure of the bias signal P and the power fluid average pressure F The differential pressure input signal P P is assumed to be of magnitude sufficiently small such that small signal operation is maintained, that is, variable input signals P and P are always smaller in pressure magnitude than average pressure F by at least a factor of 2. It is further assumed that both fluid amplifiers are of identical construction and the receivers of each are in communication with identical and known loads (fluid flow restrictors) in order to obtain symmetrical push-pull operation. Nonsymmetrical push-pull operation is obtained, when desired, by employing identical amplifiers with (1) unequal receiver loads (2) unequal biases or (3) unequal power fluid average pressures, or (4) by employing nonidentical amplifiers.

An example of the variable gain characteristics of a specific push-pull arrangement of my FIGURE 1 device is illustrated in FIGURE 4 wherein each amplifier has the input-output characteristics illustrated in FIGURE 3. The variable gain characteristics illustrated in FIGURE 4 were obtained at a power fluid average supply pressure F of 9 p.s.i.g. The device also functions satisfactorily at lower average supply pressures as long as the bias pressure is high relative to (but less than) F. The variable gain characteristics for the push-pull device of FIGURE 1 is illustrated for three different bias pressures in FIG- URE 4. The bias pressures P P and P are 1.8, 3.0, and 4.2 p.s.i., respectively. The abscissa and ordinate of the FIGURE 4 graph are in terms of p.s.i. differential pressure. Thus, it can be seen that for small signal operation of approximately 12.0 p.s.i. differential pressure of the variable input signals P ;P a controllably variable gain is obtained as a function of the bias signal pressure P In particular, the change in gain for the exemplified bias pressure change from 4.2 to 1.8 p.s.i.g. is approximately 5:1; the change in gain for a bias pressure change from 4.5 to 1.8 p.s.i.g. is approximately 8:1. The particular i2 p.s.i. small signal range of operation is, of course, obtained for a fluidic device having a specific construction and the above-enumerated power fluid supply pressure. For other constructions of the fluidic device, or for other power fluid supply pressures, the small signal operating range may be less or greater than 2 p.s.i.

From the foregoing description, it can be appreciated that my invention makes available a new variable gain fluidic device which provides a controllably variable gain as a function of the pressure of a bias signal generating a jet of fluid coplanar with a power jet which represents an input signal to be amplified. Gains limited to less than unity are obtained by means of the bias signal which determines the operating region of the input signal, and the bias signal in combination with the average pressure of the power fluid signal determines the operating point of the fluid amplifier with respect to the control inputoutput characteristic curves of the fluid amplifier. A single fluid amplifier comprises my device when employing only single-sided input signals where as a push-pull arrangement of two such amplifiers is employed for the more usual differentially pressured input signals employed in analog-type fluidic circuitry.

Having described a particular embodiment of my variable gain fluidic device, it is believed obvious that modification and variation of my invention is possible in the light of the above teachings. Thus, the control nozzles may be disposed at any angle other than with respect to the power nozzle, but still being coplanar therewith, it being understood that the 90 jet intersecting relationship provides the maximum degree of jet deflection.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A two-dimensional flow, variable gain fluidic device comprising a first fluid amplifier of the analog type, said first fluid amplifier comprising first means for generating a pressurized first jet of fluid,

first means for generating a pressurized first jet generating means and aligned with the centerline axis thereof for receiving the first fluid jet, said first receiver being the only receiver in said first amplifier and disposed in direct fluid communication with said first generating means,

second means for generating a pressurized second jet of fluid adjustable in pressure within a predetermined range of pressures and independent of the source of fiuid of the first jet for controllably deflecting by momentum exchange the first jet relative to said first receiver,

first venting means intermediate said first receiver and said second generating means for relieving fluid pressure adjacent said first receiver, and

second venting means intermediate said first receiver and said first generating means and disposed in opposing relationship to said first venting means for further relieving fluid pressure adjacent said first receiver, and

a second fluid amplifier of the analog type to provide push-pull operation of said device, said second fluid amplifier comprising third means for generating a pressurized third jet of fluid,

a second fluid receiver downstream from said third generating means and aligned with the centerline axis thereof for receiving the third fluid jet, said second receiver being the only receiver in said second amplifier and disposed in direct fluid communication with said third generating means,

fourth means for generating a pressurized fourth jet of fluid adjustable in pressure within a predetermined range of pressures and independent of the source of fluid of the third jet for controllably deflecting by momentum exchange the third jet relative to said second receiver, the second and fourth jets representing bias signals determining the operating regions of the device relative to the nonlinear input-output characteristic curves of said first and second fluid amplifiers, the gain of said first and second fluid amplifiers being a function of the bias signals and being controllably variable by adjustment of the pressures thereof, the differential pressure of the fluid received in said first and second receivers being the output of said device, the output pressure in each amplifier being maximum at zero bias pressure and decreasing with increased bias pressure,

third venting means intermediate said second receiver and said fourth generating means for relieving fluid pressure adjacent said second receiver, and

fourth venting means intermediate said second receiver and said third generating means and disposed in opposing relationship to said third venting means for further relieving fluid pressure adjacent said second receiver.

2. The variable gain push-pull fluidic device set forth in claim 1 wherein said first and second fluid amplifiers are of identical construction, and

said second and fourth generating means in communication with a common source of pressurized fluid independent of the source of fluid of the first and third jets and adjustable in pressure within a predetermined range of pressure whereby said first and second fluid amplifiers function at the same bias pressure.

3. The variable gain fluidic device set forth in claim 1 wherein said first and third generating means comprise first fluid passages in communication with a first source of pressurized fluid at first ends thereof and terminating in first and third fluid flow restrictors, respectively, for issuing the first and third jets at second ends thereof, and

said second and fourth generating means comprise second fluid passages in communication with a common second source of pressurized fluid independent of the first source and adjustable in pressure at first ends 8 thereof and terminating in second and fourth fluid flow restrictors, respectively, for issuing the second and fourth jets at second ends thereof.

References Cited UNITED STATES PATENTS 3,238,959 3/1966 Bowles 137-815 3,331,379 7/1967 Bowles 137-815 3,410,291 11/1968 Boothe et a1. 137-815 3,080,886 3/1963 Severson 137-815 3,117,593 1/1964 Sowers 137-815 XR 3,228,410 1/1966 Warren et al. 137-815 3,279,488 10/1966 Jones 137-815 3,285,264 11/1966 Boothe 137-815 3,338,515 8/1967 Dexter 137-81.5 XR 3,340,885 9/1967 Bauer 137-815 3,348,562 10/1967 Ogren 137-815 3,350,008 10/ 1967 Avery.

SAMUEL SCOTT, Primary Examiner US. Cl. X.R. 235-201 

